It is often desirable to assess the intracranial pressure of a patient. For example, in the course of treatment of hydrocephalus the estimation of intracranial pressure is a useful tool for the assessment of shunt malfunction. By way of further example, patients with cerebral edema secondary to head trauma often suffer from increased intracranial pressure, and it is necessary to measure or estimate such pressure in order to diagnose and treat the increased intracranial pressure.
At present, intracranial pressure can be measured only by invasive techniques. For example, one common technique for measuring intracranial pressure involves the insertion of a pressure transducer directly into the epidural space through a burr hole. The pressure may then be displayed and recorded using conventional techniques. In shunted hydrocephalic patients, intracranial pressure may be measured manometrically by direct puncture of the shunt. Invasive methods of intracranial measurements suffer from numerous draw backs, including the trauma involved in placing measurement devices, as well as the time involved in using such equipment.
Visual evoked potentials are electrical brain signals which are caused by visual stimulation, such as the observance of a flashing light. The characteristics of visual evoked potentials are relatively well-defined in both the maturing child and the adult. Visual evoked potentials have been used to provide information about a variety of characteristics, such as visual acuity, diseases of the optic nerve and chiasm, color blindness, and other problems of vision. Visual evoked potentials are also used to monitor surgery around the optic nerves and chiasms and to assess effects of hypotension and brain retraction. Evidence of edema, contusion or other traumas within the temporal, parietal, and occipital lobes has been demonstrated by using visual evoked potentials. Visual evoked potential measuring has also been used to determine a variety of other brain-related characteristics, such as intelligence, brain memory, sensory perception, and local dysfunction.